For SF/Fantasy backlist, try
BookViewCafé. It's a consortium of established authors, some of them quite well known like Vonda McIntyre and Sherwood Smith and Judith Tarr, selling their older works in MultiFormat, DRM-free editions.
Average price is $4.99 per book, plus they've put up plenty of short stories and novellas for free reading and you'll basically be supporting the authors directly. Ursula K. Le Guin even has a couple of things up there, though none of her famous classic stuff, of course.